The present invention, as defined, involves the bonding of a semiconductor device (chip) to a circuitized substrate, the substrate preferably a printed circuit board. Typically, such boards are comprised of dielectric material such as epoxy resin reinforced with fiberglass, and include a plurality of conductive layers (referred to as signal, power and/or ground planes) as part thereof. One particular advantage of directly bonding a semiconductor chip onto a printed circuit board is the elimination of an interim substrate as has been typically used in the art, one example being referred to as a flexible (or thin) film carrier. Such a carrier is described in the aforementioned U.S. Pat. No. 5,057,969, as well as in U.S. Pat. Nos. 4,937,006, 4,962,416 and 4,914,551, the disclosures of which are incorporated herein by reference.
In the structures defined in these patents and application, the chip is typically bonded initially to the conductive leads (e.g., copper) of the carrier and this chip-carrier subassembly is then bonded to respective circuit (contact) sites or members on the next substrate (typically, a printed circuit board). This combined structure is then typically incorporated into the remaining electrical portions of a larger assembly (e.g., a processor) which in turn may form part of an information handling system (also known as a computer). In the processes for achieving such bonding between chip and carrier, as well as in processes wherein chips have been directly bonded to other circuitized substrates (e.g., metallized ceramic substrates), solder connections have often been utilized with hot gas directed onto the lead and/or solder junctions. U.S. Pat. No. 4,937,006 defines such a process. U.S. Pat. No. 5,057,969 also defines use of hot gas impingement, but primarily onto the copper leads, which in turn assist in heating portions of the respective solder mounds to which these are engaged. Such direct hot gas impingement onto the circuitry and adjoining surface of an epoxy resin dielectric circuit board may prove deleterious because of the lower melting point of this dielectric, in comparison to the much higher temperature ceramic and similar substrate materials.
Understandably, elimination of an interim carrier thus results in a substantial reduction in the processes, costs and time involved in making such products. As defined herein, the invention provides such distinct advantages over processes and structures as described in the foregoing patents and application in a new and unique manner. Significantly, the invention provides such connections without direct gas impingement onto the solder elements (also referred to as solder mounds or solder balls) used to form such connections. Because an interim carrier is eliminated, the conductive (copper) leads associated therewith are also removed, such that the method of connection provided by the instant invention is directly between the chip's solder elements and circuitry located on the surface of the substrate to which the chip is to be bonded. Of further significance, the avoidance of direct hot gas impingement on leads and/or substrate (including the circuitry thereof) enables direct device attachment to less costly substrates of lower melting point dielectrics (e.g., epoxy resin).
It is believed that such a form of connection will constitute a significant advancement in the art.